Method and device for providing high data rate for a serial peripheral interface

Abstract

An improved high performance scheme is provided with a serial peripheral interface (SPI) to enable microcontroller-based products and other components and devices to achieve a higher serial transmit and receive data rate. An exemplary technique utilizes a CPU and an SPI having a circular FIFO structure. To prevent the memory traffic associated with any SPI accesses from conflicting with other CPU memory accesses, the technique utilizes cycle stealing direct memory access techniques for SPI data transfers with the memory. During a CPU read/write sequence, data is read/written from/to the memory through a virtual special function register (SFR). Once the virtual SFR access is detected, all accesses are redirected to the circular FIFO buffer memory, with no additional pipelining necessary. The CPU pointers can suitably increment as appropriately controlled by hardware. In addition, once an SPI transmit/receive request is made, data communication can be established between the transmit/receive buffer and the memory. To avoid structural hazard, the transmit/receive request can be suitably pipelined until the next available clock phase, for example, within one instruction cycle. As a result, for a 4 Mhz clock rate, the technique can enable a significantly higher data transfer rate, e.g., at 250 Kbytes per second, an improvement of almost twenty times the prior art data rates. The high performance technique also avoids the firmware overhead with minimum hardware control cost. For example, compared to the hardware approach using deeper buffer structures, e.g., with FIFO buffers implemented using flip-flop devices, the exemplary techniques utilize memory, e.g., dynamic or static random access memory (DRAM or SRAM) with direct memory access (DMA).

What is claimed is:  
     
       1. A microcontroller for industrial control comprising: 
       a central processing unit (CPU);  
       a bus interface in communication with the CPU;  
       a CPU memory module in communication with the bus interface; the CPU memory module configured to include a FIFO memory buffer;  
       a direct memory access module in communication with the bus interface; and  
       a serial peripheral interface (SPI) module In communication with the direct memory access module and the bus interface; the SPI module having hardware configured to maintain pointers to addresses within the FIFO memory buffer; the SPI module hardware configured to maintain counters; and the SPI module configured to use the FIFO memory buffer, pointers and counters as a transmission buffer for external communications for creating a virtual special function register.  
     
     
       2. The microcontroller of  claim 1  the SPI module further comprising a transmitter buffer and a receiver buffer; wherein the transmitter buffer is configured to transmit data from the FIFO memory buffer, and wherein the receiver buffer is configured to transmit data to the FIFO memory buffer. 
     
     
       3. The microcontroller of  claim 1  the SPI module further configured to operate as one of a master device and a slave device. 
     
     
       4. The microcontroller of  claim 1  the SPI module further configured to provide a data register chip select signal. 
     
     
       5. The microcontroller of  claim 1  the SPI module further configured to provide at least one of a CPU transmitter pointer signal, a CPU receiver pointer signal, a SPI transmitter pointer signal and a SPI receiver pointer signal. 
     
     
       6. The microcontroller of  claim 1  wherein said direct memory access module is configured to communicate with the SPI module and the bus interface for providing cycle stealing.